Anode for secondary battery, having optimized binder distribution, and secondary battery comprising same

ABSTRACT

An anode for a non-aqueous electrolyte secondary battery includes: an anode current collector; and an anode mixture layer formed on the anode current collector, containing an anode active material, a conductor, a rubber-based binder, and a water-soluble polymer-based binder. The anode mixture layer comprises, relative to a total weight thereof, 1.0-2.5 wt % of the rubber-based binder and 0.5-1.5 wt % of the water-soluble polymer based binder. When the anode mixture layer is divided into ten equal parts in the thickness direction based on the current collector, a ratio (CA/CB) at an interval of 0 to 3 of a content ratio (CA) of the rubber-based binder to a total content of the rubber-based binder to a content ratio (Cu) of the water-soluble polymer-based binder to a total content of the water-soluble polymer-based binder is larger than 1.0, and a ratio (CA/CB) at an interval of 7 to 10 is smaller than 1.0.

TECHNICAL FIELD

The present disclosure relates to an anode for a secondary battery, morespecifically to a technology for enhancing battery performance byimproving binder distribution in terms of an anode for a secondarybattery.

BACKGROUND ART

Mobile information terminals, such as mobile phones, laptop computersand tablet computers, have been rapidly improving in functionality,compactness and weight. reduction. As a driving power source for such.terminals, a non-aqueous electrolyte secondary battery having highcapacity and high energy density is being widely used.

As an anode active material of the non-aqueous electrolyte secondarybattery, carbon materials are widely used. Due to increasing demand forhigh capacity of such non-aqueous electrolyte secondary batteries,however, silicon materials having higher discharge capacity, compared tocarbon materials, are drawing attention.

As a technique for a non-aqueous electrolyte secondary battery using asilicon material, Japanese Patent No. 6128481 discloses that in anon-aqueous electrolyte secondary battery having an anode plate on whichan anode active material layer having an anode active material and abinder is formed on an anode body, the anode active material includes asilicon oxide and a carbonaceous material, a mass of the silicon oxideis 1% to 20% by mass with respect to a sum of the silicon oxide mass anda carbonaceous material mass, and a ratio (O/Si) of an oxygen atom overa silicon atom of the silicon oxide is 0.5 to 1.5, the binder includes abinder A formed of a rubber having a double bond and a binder B formedof a water-soluble polymer compound, wherein the binder A is distributedmore in the anode body as compared to on a surface of the anode activematerial layer, and the binder B is present at least around the siliconoxide.

The JP patent specifies distributions of the binders A and B on an anodeplate including SiOx, but is silent on contents thereof.

DISCLOSURE Technical Problem

It is common that in an anode of a non-aqueous electrolyte secondarybattery, a rubber-based binder and a water-soluble polymer-based binderare used to maintain binding force between an anode active material andan anode current collector. In consideration of effects of the binderson the binding force, the aim of the present invention is to improvequality and performance of a product by optimizing a distribution ofeach binder for each electrode position as compared to the case of usingthe same amount of the binders.

Technical Solution

The present invention provides an anode for a non-aqueous electrolytesecondary battery, including an anode current collector; and an anodemixture layer formed on the anode current collector and comprising ananode active material, a conductive material, a rubber-base binder and awater-soluble polymer-based binder, wherein the anode mixture layercomprises 1.0 wt % to 2.5 wt % of the rubber-based binder and 0.5 wt %to 1.5 wt % of the water-soluble polymer-based binder, based on a totalweight of the anode mixture layer, and when the anode mixture layer isdivided into 10 equal parts in a thickness direction starting from asurface of the anode current collector, a ratio (C_(A)/C_(B)) of acontent ratio (C_(B)) of the rubber-based binder at intervals of part 0to 3 to a total content of the rubber-based binder to a content ratio(C_(B)) of the water-soluble polymer-based binder at intervals of part 0to 3 to a total content of the water-soluble polymer-based binder isgreater than 1.0, and a ratio (C_(A)/C_(B)) at intervals of part 7 to 10is smaller than 1.0.

It is preferable that a content of the rubber-based binder be greater atthe intervals of part 0 to 3 than at the intervals of part 7 to 10.

It is preferable that the C_(A)/C_(B) of the intervals of part 0 to 3 be1.02 to 1.50 and the C_(A)/C_(B) of the interval of part 7 to 10 be 0.50to 0.98. It is also preferable that the C_(A)/C_(B) of the intervals ofpart 0 to 3 be 1.07 to 1.48 and the C_(A)/C_(B) of the intervals of part7 to 10 be 0.52 to 0.95.

A content of the rubber-based. binder may be greater at the intervals ofpart 0 to 3 and smaller at the intervals of part 1 to 10 as compared toa total content thereof in an entire interval.

The rubber-based binder may be at least one selected from. the groupconsisting of a styrene butadiene rubber (SBR), a fluorine-based rubber,an ethylene propylene rubber, a butyl acrylate rubber, a butadienerubber, an isoprene rubber, an acrylonitrile rubber, an acrylic-basedrubber and a silane-based rubber.

The water-soluble polymer-based binder may be at least one selected fromthe group consisting of carboxymethylcellulose, cellulose,polyvinylpyrrolidone, polyvinyl alcohol, polyacrylate and derivativesthereof.

The anode active material may be at least one selected from the groupconsisting of natural graphite or artificial graphite, soft carbon hardcarbon and a silicon oxide, and the conductive material may be at leastone selected from the group consisting of acetylene carbon black,Ketjenblack, carbon nanotubes, graphene and graphite.

The anode mixture layer may have a ratio (C_(A)/C_(B)) greater than 1.0at intervals of part 3 to 5, and a ratio (C_(A)/C_(B)) smaller than 1.0at intervals of part 5 to 7.

Further, the present invention provides a non-aqueous electrolytesecondary battery including the anode described above.

Advantageous Effects

According to the present invention, an anode can alleviate peeling of ananode mixture layer from an anode current collector as well as improvingbattery performance.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating a concept regardingdiffusion of lithium ions in accordance with a content distribution of arubber-based binder in a thickness direction of an anode mixture layer.

FIG. 2 is a graph illustrating content ratios (C/C_(avg)) andC_(A)/C_(B) in each interval with respect to an average SBR and CMCcontent in an entire section in Comparative Example 1.

FIG. 3 is a graph illustrating content ratios (C/C_(avg)) andC_(A)/C_(B) in each interval with respect to an average SBR and CMCcontent in an entire section in Example 1.

FIG. 4 are photographic images of the permeation of distilled water intoan electrode according to an electrode peeling experiment on an anodesurface and peeling according thereto in Comparative Example 1 andExample 1.

BEST MODE

The present invention relates to a non-aqueous electrolyte secondarybattery including an anode mixture layer formed by applying an anodeactive material, a rubber-based binder and a water-soluble polymer basedbinder onto an anode current collector.

Specifically, the anode provided herein includes an anode currentcollector and an anode mixture layer formed on the anode currentcollector and including an anode active material, a conductive material,a rubber-base binder and a water-soluble polymer-based binder appliedthereto.

The binders basically serve to maintain adhesion between the anodeactive materials and adhesion between the active materials and the anodecurrent collector. The anode mixture layer includes 1.0 wt % to 2.5 wt %of the rubber-based binder and 0.5 wt % to 1.5 wt % of the water-solublepolymer-based binder based on a. total weight of the anode mixturelayer.

When a total amount of the rubber-based binder included in the anodemixture layer is less than 1.0 wt %, the adhesion between the anodeactive materials may be deteriorated. Also, due to insufficientductility of the anode mixture layer, cracking may readily occur duringa drying or rolling process. When the amount exceeds 2.5 wt %, movementsof electrons and lithium ions in the battery may be inhibited, therebysignificantly increasing cell resistance.

The rubber-based binder is not particularly limited, but may be at leastone selected from the group consisting of a styrene butadiene rubber(SBR), a fluorine-based rubber, an ethylene propylene rubber, a butylacrylate rubber, a butadiene rubber, an isoprene rubber, anacrylonitrile rubber, an acrylic-based rubber and a silane-based rubber.

When an amount of the water-soluble polymer-based binder in the anodemixture layer is less than 0.5 wt %, not only the adhesion between theanode active materials is deteriorated but also viscosity of a slurry isreduced, thereby leading to problems such as reduced phase stability ofthe slurry and an increased thickness of an edge portion during coating.in contrast, when the amount exceeds 1.5 wt %, viscosity of the slurryexcessively increases, which leads to reduced coating processability andmakes it difficult to dissolve the water-soluble polymer-based binder,thereby forming micro-gel.

The water-soluble polymer-based binder may be at least one selected fromthe group consisting of carboxymethlcellulose, cellulose,polyviylpyrrolidone, polyvinyl alcohol, polyacrylate and derivativesthereof.

Meanwhile, the anode mixture layer of the present invention includes ananode active material and a conductive material in addition to therubber-based and water-soluble polymer-based binders. The anode activematerial and the conductive material may be any one of materialsconventionally used and may be included in any amount conventionallyemployed in formation of an anode mixture layer, and is riotparticularly limited herein.

As the anode active material, a graphite-based material, anon-grate-based material and silicon oxides may be used. Examples of thegraphite-based material are natural graphite, artificial graphite, andthe like. Those of the non-graphite-based material are soft carbon, hardcarbon, and to the like. These can be used independently, or two or morethereof may be combined to use.

Examples of the conductive material are carbon black, Ketjen black, acarbon nanotube, graphene, graphite, and the like. Any of these carbonmaterials can be used independently, or two or more thereof can becombined for use.

As described above, the anode mixture layer is manufactured by addingwater to a mixture of the anode active material, the conductivematerial, and the rubber-based and the water-soluble polymer-based.binders to prepare a slurry and applying the slurry onto the anodecurrent collector followed by drying. Although not particularly limited,the water, for example, distilled water, may be contained. in an amountrange of 40 wt % to 60 wt %, based on a total weight of the slurry.

The anode mixture layer obtained by the present. invention allows theanode active materials to adhere to each other and to the anode currentcollector by the water-soluble polymer-based and rubber-based binders.

The water-soluble polymer-based binder has high affinity to water, whichleads to swelling by absorbing moisture when exposed thereto. When acomparatively large amount of such water-soluble polymer-based bindersare present on an interface of the anode mixture layer and the anodecurrent collector, a portion of the mutual adhesion among the anodeactive material, the binder and the anode current collector is replacedwith mutual adhesion between the moisture and the binders. This maydeteriorate the adhesion between the anode active material and the anodecurrent collector. Such deterioration of the adhesion may serve topeeling of the anode mixture layer from the anode current collector whenan electrolyte solution is charged.

Meanwhile, the rubber-based binder has low affinity to moisture and thusdoes not create a problem of deteriorated adhesion due to moistureabsorption as the above. Accordingly, it is more preferable that arubber-based binder is used rather than a water-soluble polymer-basedbinder at an interval close to the anode current. collector to improveadhesion between the anode active material and the anode currentcollector, that is, an anode body.

Meanwhile, the rubber-based binders are non-uniformly present among theanode active materials in the form of small particles. When suchrubber-based binders are present in a large amount on the anode mixturelayer, particularly a surface of the anode mixture layer, surface poresbetween the anode active materials are suppressed, and the lithium ionsdelivered from a cathode are suppressed. from being diffused into theanode.

The concept of the diffusion of lithium ions in accordance with acontent distribution of the rubber-based binder is schematicallyillustrated in FIG. 1. As illustrated in FIG. 1, the rubber-basedbinders present on a surface of the anode mixture layer in a largeamount interferes with delivery of lithium ions and inhibits diffusionof the lithium ions into the anode.

As a result, the battery resistance increases, or charging/dischargingefficiency decreases due to lithium plating formed on an electrodesurface during high rate charging. When the amount of the rubber-basedbinder present on the surface is small, however, the lithium ions can beeasily diffused into the anode, thereby preventing such a problem.

As described above, each of the rubber-based binders and water-solublepolymer-based binders have different effects on adhesion and batteryperformance. As such, a distribution of each binder is optimized inconsideration of such effects, to improve product quality andperformance.

In this regard, the present invention provides an anode in which, interms of the anode mixture layer, functions of the rubber-based binderare enhanced in a current collector side to alleviate peeling of theanode mixture layer from the current collector and functions of thewater-soluble polymer-based binder are enhanced on the anode mixturelayer surface to improve performance of the secondary battery, withoutsuppressing the adhesion between the active materials.

More specifically, it is preferable that the anode mixture layer of thepresent invention, when divided into 10 equal parts in a thicknessdirection starting from a surface of the anode current collector, have aratio (C_(A)/C_(B)) of a content ratio (C_(A)) of the rubber-basedbinder at intervals of part 0 to 3 to a total content of therubber-based binder to a content ratio (C_(A)) of the water-solublepolymer-based binder at intervals of part 0 to 3 to a total content ofthe water-soluble polymer-based binder of greater than 1.0, and a ratio(C_(A)/C_(B)) at intervals of part 7 to 10 of smaller than 1.0. It ismore preferable that the C_(A)/C_(B) of the intervals of part 0 to 3 be1.02 to 1.50, further more preferably 1.07 to 1.48, and the C_(A)/C_(B)of the intervals of part 7 to 10 be 0.50 to 0.98, further morepreferably 0.52 to 0.95. In this case, C_(A) or C_(B), a content ratioof the rubber-based binder or the water-soluble polymer-based binder,means a value obtained by dividing a content of each binder in acorresponding interval by a content thereof included in an entireinterval.

The interval is specified to the intervals of part 0 to 3 and that of 7to 10 because quality and performance of a product, which are to beimproved in the present invention, are related to characteristics ofboth side interfaces of the mixture layer. A desired level of thequality and performance of a product may be sufficiently achieved, whenthe above requirements are met in said intervals.

In this case, it is preferable that a content of the rubber-based binderbe greater at the intervals of part 0 to 3 than at the intervals of part7 to 10. In addition, it is preferable that a content of therubber-based binder be greater at the intervals of part 0 to 3 andsmaller at the intervals of part 7 to 10 as compared to a total contentthereof in an entire interval. Otherwise, to satisfy the distribution inwhich the C_(A)/C_(B) is greater than 1.0 at the intervals of part 0 to3 and the C_(A)/C_(B) is less than 1.0 at the intervals of part 7 to 10,a variation breath of contents of the water-soluble polymer-based binderneeds to be increased in each interval. In contrast to the rubber-basedbinder, which is water-insoluble, the water-soluble polymer-base bindermay have significantly varying viscosity of a slurry prepared inaccordance with the content variation. Accordingly, there is anincreasing likelihood that a defect may occur during a coating processrequiring uniform slurry viscosity.

Further, a ratio (C_(A)/C_(B)) of a content ratio (C_(A)) of therubber-based binder to a content ratio (C_(B)) of the water-solublepolymer-based binder may be greater than 1.0 at intervals of part 3 to 5and smaller than 1.0 at intervals of part 5 to 7.

According to the present invention, in terms of the binder distributionof the anode mixture layer, the rubber-based binder is controlled suchthat a content thereof is higher in an anode current collector side thanin an anode mixture layer surface side, while the water-solublepolymer-based polymer is controlled such that a content thereof ishigher in an anode mixture layer surface side than in an anode currentcollector side. This will serve to alleviate peeling of the anodecurrent collector from the anode mixture layer while improving batteryperformance.

A method for forming the anode mixture layer is riot particularlylimited. For example, as previously described, an anode mixturelayer-forming slurry (slurry 1) containing a binder content appropriatefor the intervals of part 0 to 3 and an anode mixture layer-formingslurry (slurry 2) containing a binder content appropriate for theintervals of part 7 to 10 are prepared, and applied to a copper foil asan anode current collector simultaneously or in order, and dried toprepare the anode mixture layer. The anode mixture layer may be preparedby applying and drying the slurry 1 first followed by applying anddrying the slurry 2.

MODE FOR INVENTION

Hereinafter, the present disclosure will be described in more detailwith reference to example embodiments. However, the present disclosureshould not be limited to the following example embodiments.

EXAMPLE 1

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 1.8%, 1.2%, 96% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry1.

SBR (A) and CMC (B) , as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed, such thatweight percentages thereof were 1.2%, 1.2%, 96.6% and 1%, respectively,and distilled water was added such that a weight of the solid isapproximately 52%, and mixed for 100 minutes to prepare an anode slurry2.

The anode slurry I was applied to one surface of a copper foil (8μm-thickness) at a thickness of 60 μm to form a first mixture layer. Theanode slurry 2 was then applied on the first mixture layer at athickness of 60 μm to form a second mixture layer.

The first mixture layer at intervals of part 0 to 5 and the secondmixture layer at intervals of part 5 to 10 were formed in a thicknessdirection based on a surface of the copper foil, and dried in a dryingchamber consisting of 4 sections:

Section 1: temp 100° C., air speed 0.42 m/s, drying time 20 sec

Section 2: temp 110° C., air speed 0.47 m/s, drying time 20 sec

Section 3: temp 115° C., air speed 0.50 m/s, drying time 20 sec

Section 4: temp 125° C., air speed 0.77 m/s, drying time 20 sec.

The first and second mixture layers (while on the foil) were thencalendered to prepare an anode having a final thickness of 80 μm.

EXAMPLE 2

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 1.8%, 1.3%, 95.9% and 1%, respectivelyand distilled water was added such that a weight of a solid wasapproximately 52%, and mixed for 100 minutes to prepare an anode slurry1.

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight. percentages thereof were 1.2%, 1.3%, 96.5% and 1%, respectively,and distilled water was added such that a weight of the solid wasapproximately 52%, and mixed for 100 minutes to prepare an anode slurry2.

An anode having the anode mixture layer on the copper foil surface wasprepared using the same method as in Example 1.

EXAMPLE 3

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such. thatweight percentages thereof were 1.8%, 1.2%, 96% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry1.

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 0.8%, 1.2%, 97% and 1%, respectively,and distilled water was added such that a weight of the solidsapproximately 50%, and mixed for 100 minutes to prepare an anode slurry2.

An anode having the anode mixture layer on the copper foil surface wasprepared using the same method as in Example 1.

EXAMPLE 4

SBR (A) and CMC (B), as hinders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 1.8%, 1.2%, 96% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry1.

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 0.8%, 1.2%, 97% and 1%, respectively,and distilled water was added such that a weight of the solid isapproximately 50%, and mixed for 100 minutes to prepare an anode slurry2.

The anode slurry 1 was applied to one surface of a copper foil (8μm-thickness) at a thickness of 60 μm and dried in a drying chamberconsisting of 4 sections under the following conditions to form a firstmixture layer:

Section 1: temp 130° C., air speed. 2.01 m/s, drying time 10 sec

Section 2: temp 140° C., air speed 2.01 m/s, drying time 10 sec

Section 3: temp 140° C., air speed 0.60 m/s, drying time

Section 4: temp 150° C., air speed 1.01 m/s, drying time 10 sec.

The anode slurry 2 was then applied to the first mixture layer at athickness of 60 μm and dried in a drying chamber consisting of 4sections under the same conditions as how the first mixture layer wasformed, to form a second mixture layer.

A structure in which the first mixture layer was formed at the intervalsof part 0 to 5 and the second mixture layer was formed at the intervalsof part 5 to 10 in the thickness direction based on the copper foilsurface was formed.

An anode was prepared by calendaring the first and second mixture layersto have a final thickness of 80 μm.

EXAMPLE 5

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon. black as a conductive material were mixed, suchthat weight percentages thereof were 1.6%, 1.2%, 96.2% and 1%,respectively, and distilled water was added such that a weight of asolid was approximately 50%, and mixed for 100 minutes to prepare ananode slurry 1.

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 1.4%, 1.2%, 96.4% and 1%, respectively,and distilled water was added such that a weight of the solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry2.

The anode slurry 1 was applied to one surface of a copper foil (8μm-thickness) at a thickness of 60 μm and dried in a drying chamberconsisting of 4 sections under the following conditions to form a firstmixture layer:

Section 1: temp 130 ° C., air speed 2.01 m/s, drying time 10 sec

Section 2: temp 140° C., air speed 2.01 m/s, drying time 10 sec

Section 3: temp 140° C., air speed 0.60 m/s, drying time 10 sec

Section 4: temp 150° C., air speed 1.01 m/s, drying time 10 sec.

The anode slurry 2 was then applied to the first mixture layer at athickness of 60 μm and dried in a drying chamber consisting of 4sections under the same conditions as how the first mixture layer wasformed, to form a second mixture layer.

A structure in which the first. mixture layer are formed at theintervals of part 0 to 5 and the second mixture layer are formed at theintervals of part 5 to 10 in the thickness direction based cm the copperfoil surface was formed.

An anode was prepared by calendering the first and second mixture layersto have a final thickness of 80 μm.

COMPARATIVE EXAMPLE 1

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 1.5%, 1.2%, 96.3% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry1.

The anode slurry 1 was applied to one surface of a copper foil (8μm-thickness) at a thickness of 120 μm and dried in a drying chamberconsisting of 4 sections under the following conditions to form a firstmixture layer in a thickness intervals of part 0 to 10:

Section 1: temp 100° C., air speed 0.42 m/s, drying time 20 sec

Section 2: temp 110° C., air speed 0.47 m/s, drying time 20 sec

Section 3: temp 115° C., air speed. 0.50 m/s, drying time 20 sec

Section 4: temp 125° C., air speed 0.77 m/s, drying time 20 sec.

Thus-prepared mixture layer was calendered to prepare an anode having afinal thickness of 80 μm.

COMPARATIVE EXAMPLE 2

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such that.weight percentages thereof were 1.5%, 1.3, 96.2% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 52%, and mixed for 100 minutes to prepare an anode slurry1.

The anode slurry 1 was applied to one surface of a copper foil (8μm-thickness) at a thickness of 120 μm and dried under the sameconditions in Comparative Example 1 to form a first mixture layer in athickness intervals of part 0 to 10.

Thus-prepared first mixture layer was calendered to prepare an anodehaving a final thickness of 80 μm.

COMPARATIVE EXAMPLE 3

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 0.8%, 1.2, 97% and 1%, respectively, anddistilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry1.

The anode slurry was applied to one surface of a copper foil (8μm-thickness) at a thickness of 120 μm and dried under the sameconditions in Comparative Example 1 to form a first mixture layer in athickness intervals of part 0 to 10.

Thus-prepared first mixture layer was calendered to prepare an anodehaving a final thickness of 80 μm.

COMPARATIVE EXAMPLE 4

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 1.8%, 1.2%, 96% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry1.

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight. percentages thereon were 1.2%, 1.2%, 96.6% and 1%, respectively,and distilled water was added such that a weight of the solid isapproximately 52%, and mixed for 100 minutes to prepare an anode slurry2.

The anode slurry was applied to one surface of a copper foil (8μm-thickness) at a thickness of 60 μm to form a first mixture layer. Theanode slurry 2 was then applied to the first mixture layer at athickness of 60 μm to form a second mixture layer.

The first mixture layer at intervals of part 0 to 5 and the secondmixture layer at intervals of part 5 to 10 are formed in a thicknessdirection based on a surface of the copper foil, and dried in a dryingchamber consisting of 4 sections:

Section 1: temp 130° C., air speed 2.01 m/s, drying time

Section 2: temp 140° C., air speed. 2.01 m/s, drying time 10 sec

Section 3: temp 140° C., air speed 0.60 m/s, drying time 10 sec

Section 4: temp 150° C., air speed 1.01 m/s, drying time 10 sec.

The first and second mixture layers were then calendered to prepare ananode having a final thickness of 80 μm.

COMPARATIVE EXAMPLE 5

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 1.4%, 1.6%, 96% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes.

Due to high viscosity, however, no slurry was obtained, and furtherprocedures for manufacturing an anode were not performed.

COMPARATIVE EXAMPLE 6

SBR (A) and CMC (B), as binders, artificial graphite as an anode activematerial and carbon black as a conductive material were mixed such thatweight percentages thereof were 2%, 0.4%, 96.6% and 1%, respectively,and distilled water was added such that a weight of a solid wasapproximately 50%, and mixed for 100 minutes to prepare an anode slurry1.

The anode slurry 1 was applied to one surface of a copper foil (8μm-thickness) at a thickness of 120 μm. Due to low viscosity, however,the slurry did not stably form a coating layer on the copper foil. Inthis regard, further procedures for manufacturing an anode were notperformed.

Binder Distribution Measurement in Mixture Layer

A binder distribution in the thickness direction was measured withrespect to mixture layers of the anodes prepared in Examples 1 to 5 andComparative Examples 1 to 4, and results thereof are shown in Table 1.

The measurement of the binder distribution was performed by staining theanode mixture layers with OsO₄ and cutting a cross-section of theelectrode followed by performing SEM-EDAX analysis.

Distribution of an Os element in the cross-section of the mixture layerfrom the SEM analysis indicates distribution of the rubber-based binder,and that of a Na element indicates distribution of the water-solublebinder.

In Table 1, C_(A) represents a ratio of the SBR included in apredetermined section (intervals of part 1 to 3 and 7 to 10 in thethickness direction from the current collector) to a total SBR content,and represents a content ratio of the CMC in a predetermined section(intervals of part 0 to 3 and 7 to 10 in the thickness direction fromthe current collector) to a total CNC content, while C_(A)/C_(B)represents a ratio of C_(A) to C_(B) contained in a predeterminedsection (intervals of part 0 to 3 and 7 to 10 in the thickness directionfrom the current collector).

Further, in Example 1 and Comparative Example 1, a content ratio(C/C_(avg)) of the SER or the CNC content to an average SBR content oran average CMC content in an entire interval and C_(A)/C_(B) are shownin FIGS. 2 and 3, respectively. In FIGS. 2 and 3, (A) is a graph ofC/C_(avg), and (B) is a graph of C_(A)/C_(B).

Current Collector Adhesion Measurement

In order to measure adhesion between the mixture layer and. the currentcollector in the electrodes prepared in Examples 1 to 5 and ComparativeExamples 1 to 4, 18 mm-wide 3M tape was attached to each electrode, anda 90° peel test was performed.

Load values were measured when the mixture layer and the currentcollector were separated from each other, and the current collectoradhesion was calculated by dividing the load values by the width of thetape, which are shown in Table

Measurement of Electrode Peeling

The electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to4 were cut into a size of 5 cm×5 cm, and four corners were fixed withtape.

About 1 mL of distilled water was dropped on the mixture layer of theelectrode, and allowed to sit for 30 minutes.

Observation was performed with regard to whether distilled waterpenetrated into the mixture layer and to peel the mixture layer from thecurrent collector with naked eye, which is denoted as ∘ (peeled) and ×(unreeled) in Table 1.

Battery Charging/Discharging Efficiency Measurement

Batteries were manufactured using the electrodes prepared in Examples 1to 5 and Comparative Examples 1 to 4.

Each battery was charged in a constant current (CC) mode of 1.5 C untila voltage thereof reached 4.2V, and charged capacity was measured.

Discharging was performed in a CC mode of 0.3 C until the voltagereached 2.5V, and the discharge capacity was measured.

Thus-measured discharging capacity was divided by the charging capacityto calculate the charging/discharging efficiency, and results thereofare shown in Table 1.

TABLE 1 Comp. Example Example Items 1 2 3 4 1 2 3 4 5 Total binder SBR(A) 1.5 1.5 0.8 1.5 1.5 1.5 1.3 1.3 1.5 content (wt %) CMC (B) 1.2 1.31.2 1.2 1.2 1.3 1.2 1.2 1.2 Binder content C_(A) (%) 26 26 27 26 31 3033 41 29 ratio in C_(B) (%) 29 27 28 28 28 27 27 28 28 interval ofC_(A)/C_(B) 0.91 0.96 0.96 0.93 1.09 1.10 1.22 1.46 1.04 part 0-3 Bindercontent C_(A) (%) 37 38 36 38 26 28 24 18 30 ratio in C_(B) (%) 33 35 3333 32 31 33 32 31 interval of C_(A)/C_(B) 1.12 1.08 1.09 1.15 0.85 0.900.72 0.53 0.97 part 7-10 Current collector 0.22 0.24 0.11 0.07 0.24 0.260.23 0.33 0.23 adhesion (N/cm) Electrode peeling O O O O X X X X XCharging/Discharging 97.0 97.3 99.7 96.8 99.6 99.2 100.0 100.0 98.1efficiency (%)

As shown in Table 1 and FIGS. 2 and 3, Examples 1 to 5, the cases inwhich a content ratio C_(A) of SBR is larger than that C_(B) of CMC atthe intervals of part 0 to 3, close to the current collector(C_(A)/C_(B)>1) have excellent charging/discharging efficiency, andpeeling of the electrode, which is caused due to distilled water, didnot occur. In the case of Comparative Examples 1 and 2, however, acontent ratio C_(A) of CMC is larger than that C_(B) of SBR at theintervals of part 0 to 3, close to the current collector(C_(A)/C_(B)>1), electrode peeling occurred due to binder swellinginduced by water. An electrode peeling experiment due to distilled waterpenetration was performed on anode surfaces of Comparative Example 1 andExample 1. Penetration of distilled water into the electrodes of Example1 and Comparative Example 1 was observed, and photographic imagesthereof are shown in FIG. 4.

As shown in FIG. 4, distilled. water easily penetrated in ComparativeExample 1 due to the high CMC content ratio; however, distilled waterdid not easily penetrate in Example 1. This indicates that electrodepeeling from the current collector due to moisture penetration can beinhibited in the present invention.

The anodes of Comparative Examples 1 to 4 showed reducedcharging/discharging efficiency as compared to those of Examples 1 to 5.In the case of Comparative Examples 1 to 4, the SBR content ratio(C_(A)) was high at the intervals of part 7 to 10, an anode surfaceside, as a large amount of SBR particles fill a pore of an activematerial surface to interfere with diffusion of lithium ions into theanode.

Accordingly, in terms of the anodes of Examples 1 to 5, not only qualitybut also performance of a product can be improved by optimizing adistribution of each binder for each electrode position even when thesame amounts of binders are used.

When the SBR content is low as in Comparative Example 3, adhesion to thecurrent collector is shown to be significantly low, and a problem arisesin that the electrode mixture layer or the anode active material ispeeled from, the current collector. It can be easily predicted that inthe case of a significantly low content of the SBR, although an anodeslurry, which is control led in terms of a binder distribution, was notused in Comparative Example 3, adhesion to such a current collectorwould be significantly reduced even when a binder content is controlled.for each interval.

Meanwhile, the same anode slurry 1 and anode slurry 2 were used inComparative Example 4 as in Example 1, but under different dryingconditions. The results of Comparative Example 4 and Example 1 indicatethat even though the same anode slurry was used, distributions ofbinders present in each interval in the thickness direction of the anodemixture layer may vary according to drying conditions.

The above results indicate that by controlling the drying process, ananode having an anode mixture layer having a controlled binder contentsfor each interval can be prepared as in the present invention.

1. An anode for a non-aqueous electrolyte secondary battery, the anodecomprising: an anode current collector; and an anode mixture layerformed on the anode current collector, the anode mixture layercomprising an anode active material, a conductive material, arubber-base binder and a water-soluble polymer-based binder, wherein theanode mixture layer comprises 1.0 wt % to 2.5 wt % of the rubber-basedbinder and 0.5 wt % to 1.5 wt % of the water-soluble polymer-basedbinder based on a total weight of the anode mixture layer, and whereinwhen the anode mixture layer is divided into 10 equal intervals in athickness direction starting from the surface of the anode currentcollector, a ratio (C_(A)/C_(B)) of a content ratio (C_(A)) of therubber-based binder at an intervals of part 0 to 3 to a total content ofthe rubber-based binder to a content ratio (C_(B)) of the water-solublepolymer-based binder at intervals of part 0 to 3 to a total content ofthe water-soluble polymer-based binder is greater than 1.0, and a ratio(C_(A)/C_(B)) at intervals of part 7 to 10 is smaller than 1.0.
 2. Theanode for a non-aqueous electrolyte secondary battery of claim 1,wherein a content of the rubber-based binder is greater at the intervalsof part 0 to 3 than at the intervals of part 7 to
 10. 3. The anode for anon-aqueous electrolyte secondary battery of claim 1, wherein theC_(A)/C_(B) of the intervals of part 0 to 3 is 1.02 to 1.50 and theC_(A)/C_(B) of the intervals of part 7 to 10 is 0.50 to 0.98.
 4. Theanode for a non-aqueous electrolyte secondary battery of claim 1,wherein the C_(A)/C_(B) of the intervals of part 0 to 3 is 1.07 to 1.48and the C_(A)/C_(B) of the intervals of part 7 to 10 is 0.52 to 0.95. 5.The anode for a non-aqueous electrolyte secondary battery of claim 1,wherein a content of the rubber-based binder is greater at the intervalsof part 0 to 3 and smaller at the intervals of part 7 to 10 as comparedto a total content thereof in an entire interval.
 6. The anode for anon-aqueous electrolyte secondary battery of claim 1, wherein therubber-based binder is at least one selected from the group consistingof a styrene butadiene rubber (SBR), a fluorine-based rubber, anethylene propylene rubber, a butyl acrylate rubber, a butadiene rubber,an isoprene rubber, an acrylonitrile rubber, an acrylic-based rubber anda silane-based rubber.
 7. The anode for a non-aqueous electrolytesecondary battery of claim 1, wherein the water-soluble polymer-basedbinder is at least one selected from the group consisting ofcarboxymethylcellulose, cellulose, polyvinylpyrrolidone, polyvinylalcohol, polyacrylate and derivatives thereof.
 8. The anode for anon-aqueous electrolyte secondary battery of claim 1, wherein the anodeactive material is at least one selected from the group consisting ofnatural graphite or artificial graphite, soft carbon, hard carbon and asilicon oxide.
 9. The anode for a non-aqueous electrolyte secondarybattery of claim 1, wherein the conductive material is at least oneselected from the group consisting of acetylene carbon black,Ketjenblack, carbon nanotubes, graphene and graphite.
 10. The anode fora non-aqueous electrolyte secondary battery of claim 1, wherein theanode mixture layer has a ratio (C_(A)/C_(B)) greater than 1.0 atinterval of part 4 to 5, and a ratio (C_(A)/C_(B)) smaller than 1.0 atan intervals of part 5 to
 7. 11. A non-aqueous electrolyte secondarybattery, comprising the anode of claim
 1. 12. The non-aqueouselectrolyte secondary battery of claim 11, wherein the anode mixturelayer has a ratio (C_(A)/C_(B)) greater than 1.0 at intervals of part 3to 5, and a ratio (C_(A)/C_(B)) smaller than 1.0 at intervals of part 5to
 7. 13. An anode for a non-aqueous electrolyte for a secondarybattery, the anode comprising: an anode current collector; and an anodemixture layer formed on the anode current collector, the anode mixturelayer comprising a plurality of particles made of an anode activematerial, a plurality of first and second binder particles interspersedbetween the particles of the anode active material and between theparticles of the anode active material and the anode current collector,wherein a content of the first binder particles adjacent to the anodecurrent collector is greater the content of the second binder particles,and wherein a content of the first binder particles adjacent to a topsurface of the anode mixture layer is less than the content of thesecond binder particles.
 14. The anode of claim 13, wherein the areaadjacent to the anode current collector is defined as an areacorresponding to intervals of part 0 to 3 and the area adjacent to thetop surface of the anode mixture layer is defined as an areacorresponding to intervals of part 7 to 10, wherein intervals of part 0to 10 are ten equal thickness intervals dividing the total area of theanode mixture layer.
 15. The anode of claim 14, wherein a ratio(C_(A)/C_(B)) of a content ratio (C_(A)) of the rubber-based binder atintervals of part 0 to 3 to a total content of the rubber-based binderto a content ratio (C_(B)) of the water-soluble polymer-based binder atintervals of part 0 to 3 to a total content of the water-solublepolymer-based binder is greater than 1.0, and a ratio (C_(A)/C_(B)) atintervals of part 7 to 10 is smaller than 1.0.
 16. The anode of claim13, wherein the anode mixture layer comprises 1.0 wt % to 2.5 wt % ofthe first binder particles and 0.5 wt % to 1.5 wt % of the second hinderparticles based on a total weight of the anode mixture layer.
 17. Theanode of claim 13, further comprising a conductive material selectedfrom the group consisting of acetylene carbon black, Ketjenblack, carbonnanotubes, graphene and graphite.
 18. The anode of claim 13, wherein thefirst binder particles are made of at least one material selected fromthe group consisting of a styrene butadiene rubber (SBR), afluorine-based rubber, an ethylene propylene rubber, a butyl acrylaterubber, a butadiene rubber, an isoprene rubber, an acrylonitrile rubber,an acrylic-based rubber and a silane-based rubber.
 19. The anode ofclaim 13, wherein the second binder particles are made of at least onematerial selected from the group consisting of carboxymethylcellulose,cellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylate andderivatives thereof.
 20. The anode of claim 14, wherein the anodemixture layer has a ratio (C_(A)/C_(B)) greater than 1.0 at intervals ofpart 3 to 5, and a ratio (C_(A)/C_(B)) smaller than 1.0 at intervals ofpart 5 to 7.